Answer:

Explanation:
Given that, 
Initial speed of the cart, u = 0
Let F force is applied to the cart for time  after which the car has speed v. The force on an object is given by :
 after which the car has speed v. The force on an object is given by :
F = ma
m is the mass of the cart
We need to find the speed of second cart, if the same force is applied for the same time to a second cart with twice the mass. Force becomes,



So, the speed of second cart is half of the initial speed of first cart. So, the correct option is (b).